The present invention relates to a novel lubricating grease composition improved in roll stability in the presence of water as well as thermal stability. Conventional grease compositions have failed to display a satisfactory roll stability for practical use in the presence of water, and therefore, various studies have hitherto been made with a view to overcoming this drawback.
As the means proposed for this purpose, there is, for instance, a method wherein some animal fat is mixed with grease. However, this method is defective in that the animal fat is instable so that it is apt to be transformed to fatty acid and glycerin, causing softening of the grease during the use thereof. Application of such additives as lead naphthenate and zinc rosinate has also been studied, but all these additives have fallen short of being completely effective. To cite other well-known greases effective from the view point of roll stability in the presence of water, there are a grease comprising a lithium soap consisting of wool fatty acid, stearic acid and hydroxy acid at a well-balanced compounding ratio together with a soap of Ba, Ca, Sr or the like (as disclosed in Japanese Patent Publication No. 17136/1960) and a lithium grease prepared by combining epoxide fatty acid with saturated fatty acid (as disclosed in Japanese Patent Publication No. 5172/1964). And, to cite well-known additives to serve for improvement of said stability, there are such ones as an additive comprising polyalkylene oxide-containing polyether polyole (as disclosed in Japanese Patent Publication No. 28108/1964) and an additive comprising alkoxylated alkyl phenol (as disclosed in U.S. Pat. No. 380156).